Molecular Dynamics Study On The Irradiation-induced Damage In GaAs

In the aerospace field,GaAs is the most commonly used semiconductor material for solar cells.It is extremely susceptible to be irradiated by space particles and produces a large number of microscopic crystal defects,which reduces the performance of solar cell equipments and seriously affects the reliability and service life of space vehicles.So it is very necessary to use molecular dynamics(MD)method to study the generation process of crystal defects in GaAs materials under irradiation,and the sensitivity of this process to environmental parameters,such as temperature,irradiation energy and strain,in order to provide the theoretical guidance for the protective measures with GaAs materials.The research object of this paper is GaAs materials.The research method is molecular dynamics simulation.The research content is the change of the number of defects with time during the cascade collision,the defect peak and the defect recombination rate,and the spatial distribution of crystal defects in different stages,et al.The purpose of the study is to explore the effects of different kinds of primary knock-on atoms(Ga/As PKA),different irradiation energy and temperature,and different degrees of tensile or compressive pre-strain on the above indicators.The first part of this paper studies the basic process of GaAs materials that is damaged by irradiation.It also focuses on investigating the effects of different types of PKA on the irradiation damage process.During the irradiation damage of the materials,the crystal defects are generated when PKA is excited,and a large number of vacancies and interstitial atoms can be observed.When the irradiation energy is lower than 5 ke V,the number of defects obtained by Ga PKA and As PKA is almost equal.When the irradiation energy is higher than 5 ke V,the difference between the peak of defects and the defect recombination rate becomes obvious.When the system is in the full annealing stage,PKAs of the same energy is possible to produce the same number of defects,so a higher defect recombination rate should correspond to a higher peak of defects.When the lattice temperature is about the half of the melting temperature of GaAs(675 K),the peak of defects that are excited by As PKA with 6 ke V energy is the largest.The second part of this paper studies the irradiation damage of GaAs materials under pre-strain.We selected the tensile and compressive elastic strains less than 10%,and examined the effects of elastic pre-strain on various of irradiation damage indicators under strain.For tensile pre-strain,the total energy of the system,the peak of defects,and the time that is required to reach the peak values increase with the pre-strains.But the results show that this proportional relationship is nonlinear.This is due to the more complex coupling between the thermal vibration of lattice lattice atoms and the thermal equilibrium distance between lattice lattice atoms.When the temperatures and the irradiation energies are same respectively,the increase in pre-strain will lead to an increase in the number of defects.But at the same time,there are also individual temperatures.At this temperature,the increase of pre-strain actually causes the number of defects to decrease.For compression prestrain,there are similar results as above.In the third part of this paper,the results of the previous two chapters are compared,and it is found that the number of defects generated under tensile pre-strain is larger than that under compressive pre-strain,and 725 K and 5 keV are extracted as the critical temperature and critical irradiation energy respectively in order to distinguish the effects of different PKA types.On this basis,the non-linear coupling among the thermal equilibrium distance of the lattice atoms due to temperature,the thermal vibration amplitude of the lattice atoms,and the change in the spacing of the unidirectional lattice atoms due to pre-strain are further discussed.In summary,the relationship between the irradiation conditions and the degree of damage is obtained by simulating the irradiation damage of GaAs in this paper,which provides the theoretical basis for improving the lifetime of solar cells.